A Component is added to a GameObject to provide functionality. This functionality can vary wildly.

You could add a component that renders a model at the GameObject's position. Or you could add a component that created a physics object at the GameObject's position.

You can create your own components too. This is how games are programmed. For example, you could write a component that moved an object forward when the Forward key is held down.

Adding Components

To add a component to a GameObject in editor, select the GameObject and then click on Add Component in the inspector.

To add a component to a GameObject in code

// Create
var modelRenderer = go.AddComponent<ModelRenderer>();

// Set up
modelRenderer.Model = Model.Load( "models/dev/box.vmdl" );
modelRenderer.Tint = Color.Red;

You can also GetOrAddComponent if you want it to exist if it doesn't already.

// Get or create
var modelRenderer = go.GetOrAddComponent<ModelRenderer>();

// Set up
modelRenderer.Model = Model.Load( "models/dev/box.vmdl" );
modelRenderer.Tint = Color.Green;

Querying Components

You can query a GameObject for components in multiple different ways.

// Get a multiple components of the same type
var x = go.GetComponents<ModelRenderer>();

// Get a single component from a gameobject
var x = go.GetComponent<ModelRenderer>();

// Get a single component from a gameobject, and its children
var x = go.GetComponentInChildren<ModelRenderer>();

// Get all components from a gameobject, and its children
var x = go.GetComponentsInChildren<ModelRenderer>();

// Get all components from a gameobject's ancestors and itself
var x = go.Components.GetComponentsInParent<ModelRenderer>();

// Get a single component from a gameobject's ancestors and itself
var x = go.Components.GetComponentInParent<ModelRenderer>();

Specialized Queries

If you're wanting to go even more granular:

// Get disabled components in ancestors
var x = go.Components.Get<ModelRenderer>( FindMode.Disabled | FindMode.InAncestors );

// Get all enabled components in ancestors and self
var x = go.Components.GetAll<ModelRenderer>( FindMode.Enabled | FindMode.InAncestors | FindMode.InSelf );

// Get all components on a gameobject
var x = go.Components.GetAll();

Component References

You can get component references as variables in two main ways.

// Creates a property in the inspector, you can drag any ModelRenderer from the scene in to reference it
[Property] ModelRenderer BodyRenderer { get; set; }

// References the first ModelRenderer on the same GameObject as this component, or creates one if none exist
[RequireComponent] ModelRenderer BodyRenderer { get; set; }

Removing Components

To remove a component from a GameObject, you call DestroyComponent(). You cannot reuse this component - at this point it is destroyed forever and you should stop using it.

var depthOfField = GetComponent<DepthOfField>();
dephOfField.Destroy();

Destroying GameObject from Component

DestroyGameObject(), nice and easy. You can also use GameObject.Destroy() if you want.